APPLICATIONS OF BACTERIOLOGY 251 



cerebro-spinal fluid, urine, faeces, all may be examined. Such 

 observations are completed by cultivating and experimental 

 inoculations. 



Direct Diagnosis of the Microbe. — This has to suffice 

 when it is a microbe which cannot be cultivated. It is 

 sufficient when the microbe has characteristics which cannot be 

 mistaken. The sight of the malarial parasite of Laveran, 

 of a filaria embryo, of a trypanosome (in man) is a certain 

 diagnosis. Medicine has profited by every step in advance 

 in technique : the ultra-microscope now permits us to see 

 trypanosomes and spirochaetes living and motile much more 

 easily than with the best microscope. 



Pasteur's method of "seeding'' silk-worms was based on 

 direct diagnosis. Direct diagnosis is currently employed in 

 connection with sputum and false membranes; it is completed 

 by culture and inoculation. Inoculation is the rule when the 

 pneumococcus is observed in sputum : subcutaneously inocu- 

 lated it kills a mouse within twenty-four hours : the mouse is 

 the pneumococcus reagent. 



Blood Culture. — Blood, taken aseptically from an animal 

 not in a state of active digestion, and kept free from external 

 germs, may be kept indefinitely without putrefying. If 

 microbes develop in the blood itself or in nutrient broth 

 into which it has been put, it means that these microbes 

 existed in the blood during life. Pasteur's observations on 

 the sterility of normal blood form the foundation of the 

 diagnosis of infectious diseases by blood culture. The strepto- 

 coccus was isolated by him for the first time from the blood of 

 women suffering from puerperal fever. 



It has been proved by blood culture that gonorrhoea, which is 

 usually quite a local disease, may infect the blood with 

 gonococci and cause arthritis and endocarditis. In a frankly 

 acute pneumonia it is the rule to find pneumococci in the 

 blood. 



In typhoid fever blood cultivations have given results which 

 have upset our conceptions of this disease. It used to be 

 thought an exclusively local disease of the intestine and 



